use strict;
use warnings;

use 5.014;

say join q{}, map { sprintf q{%-10s}, $_ } 0 .. 8;
say qq{@{ [ join q{}, 0 .. 9 ] }} x 9;

my $vec = pack q{C*}, map ord, q{A} .. q{K};
say unpack q{B*}, $vec;
say qq{Total set bits - @{ [ unpack q{%32b*}, $vec ] }};

say qq{Set bits to $_ - @{ [ setBitsB4pos( \ $vec, $_ ) ] }}
   for 70 .. 87;

sub setBitsB4pos
{
    my( $rsVec, $pos ) = @_;
    my $wholeBytes = int $pos / 8;
    my $oddBits    = $pos % 8;
    my $count      = unpack q{%32b*},
       substr ${ $rsVec }, 0, $wholeBytes;

    return $count unless $oddBits;

    my $mask = pack q{C*}, ( 0 ) x $wholeBytes, do {
       my $acc;
       $acc += 2 ** ( 8 - $_ ) for 1 .. $oddBits;
       $acc;
       };
    $count += unpack q{%32b*},
       substr( ${ $rsVec }, 0, $wholeBytes + 1 ) & $mask;

    return $count;
}

##</code><code>##

0         1         2         3         4         5         6         7         8         
012345678901234567890123456789012345678901234567890123456789012345678901234567890123456789
0100000101000010010000110100010001000101010001100100011101001000010010010100101001001011
Total set bits - 31
Set bits to 70 - 23
Set bits to 71 - 23
Set bits to 72 - 24
Set bits to 73 - 24
Set bits to 74 - 25
Set bits to 75 - 25
Set bits to 76 - 25
Set bits to 77 - 26
Set bits to 78 - 26
Set bits to 79 - 27
Set bits to 80 - 27
Set bits to 81 - 27
Set bits to 82 - 28
Set bits to 83 - 28
Set bits to 84 - 28
Set bits to 85 - 29
Set bits to 86 - 29
Set bits to 87 - 30